The present invention relates to an aircraft comprising a fuselage, a wing, a main landing gear (main gear), and an engine for propelling the aircraft.
The fuselage extends along a longitudinal axis and has a rear end pointing in a reverse direction with respect to the flight direction, and a nose end pointing in the flight direction of the aircraft, which is opposite to the reverse direction. The wing is connected to the fuselage, and typically two wings are connected to opposite sides of the fuselage. The main gear is connected to the fuselage or to the wing in a main gear position with respect to the longitudinal axis. Said main gear position is located further in the reverse direction than a center of gravity of the aircraft. The term “connected” in this context also includes that the main gear is attached to a wing of the aircraft which in turn is attached to the fuselage. The main gear may include at least two main gear units at opposite traverse positions with respect to the axis of the fuselage.
Aircraft engines are provided outside of the fuselage and configured to propel the aircraft in flight. Two engines may be positioned on opposite sides of the fuselage. The engine is attached to the fuselage via an attachment device, such as a strut, in a position spaced apart from the main gear position. The attachment device is formed as a strut having a flat or streamline-shaped cross-section.
The engine, such as a gas turbine or piston engine, generates a repulsive air stream streaming in the reverse direction, which is the opposite to the direction of flight. The repulsive air stream includes any air streams generated by the engine to provide thrust to propel the aircraft in the flight. This repulsive air stream may, therefore, include any air stream generated by an air screw (also referred to as a propeller), a turbofan or combustion process inside a gas turbine engine which includes compression and expansion of a working fluid and discharges a repulsive air stream including comprise combustion gases.
Aircraft with engines attached to the fuselage are well-known, such as the DC-9 aircraft. Two possible arrangements of the tail unit are known for such aircrafts. In one arrangement, the horizontal stabilizer, including the pitch elevator, is positioned out the repulsive air stream, such as above the repulsive air stream in the case of a T-tail as used on the DC-9 aircraft. When the horizontal stabilizer is arranged outside of the repulsive air stream, it has a good stabilizing effect. However, the efficiency of the pitch elevator is reduced during low speed maneuvers, such as during take-off rotation of the aircraft.
In the second arrangement, the horizontal stabilizer including the pitch elevator is positioned to be in the repulsive air stream. In the second arrangement, the efficiency of the pitch elevator is increased due to the repulsive air stream flowing over the stabilizer. In particular, the efficiency of the pitch elevator is high while the engines are at maximum thrust. However, the stabilizing effect of the horizontal stabilizer is rather low since the horizontal stabilizer is streamlined mainly by the repulsive air stream which does not change direction with the airplane's angle of attack. Both the stabilizing effect and the elevating effect depend on the current engine thrust. In view of these disadvantages of the second arrangement, conventional wisdom was to position the horizontal stabilizer outside of the repulsive air stream, as in the first arrangement.
In the first arrangement, the efficiency of the pitch elevator is relatively low, particularly during take-off. The pitch elevator has to generate a high force for take-off rotation. But, the dynamic pressure at the pitch elevator is low due to the slow take-off speed as compared to the flight speed. To provide sufficient force for take-off rotation, the dimensions of the pitch elevator is made larger than is needed for other flight operations. A smaller pitch elevator would save weight, fuel and operational costs.
Further, aircrafts are known in the art, in particular military aircrafts, comprising thrust vector devices. Such thrust vector devices employ surface elements which can be moved into the repulsive air stream in order to deflect the repulsive air stream and cause the aircraft to rotate, e. g. for take-off rotation. However, such thrust vector devices form additional components to the aircraft which are considerably complicated to be attached to the aircraft or engine and considerably complicated to operate. Further, they introduce additional weight into the aircraft which is generally to be reduced.